Ah, the Keystone XL Pipeline. The political spin is that it will help America in two major ways: (1) it will create jobs here and (2) it will decrease our dependence on foreign oil (I guess people are conflating America and Canada, since the company constructing and primarily using it is Canadian, which makes it foreign, but perhaps since the oil would go from the tar sands to the Gulf in a pipeline that traverses our country, folks are thinking that's preferable to relying on oil from the Middle East. Or, TransCanada, the company in question, keeps stressing that some bit of the oil going through the pipeline(s)--it's more than one, people, all linked together--would actually be oil produced in America. The CEO mentions a city in Montana. Oh, and I've also heard a third reason tossed out: that the increased oil supply would lower gas and heating prices here. So, let's take each benefit in turn.
True, to construct the pipeline, there would be temporary contracting jobs given to American workers (about 42,000 people for two years). That's nothing to sneeze at in this economy, because these tend to be good jobs. However, once the pipeline is finished (parts of it are already constructed), even the CEO of TransCanada admits the number of employees needed to maintain the pipeline would be about 50. Fifty is about the number your local McDonald's hires. See here: http://www.politifact.com/punditfact/statements/2014/nov/16/russ-girling/transcanada-ceo-says-42000-keystone-xl-pipeline-jo/
Second, there is absolutely no guarantee TransCanada would sell all the oil to the United States. Why should they? Companies exist to turn a profit. So if the company can sell oil to, say, China, for more dollars a barrel, why would they give a cut-rate to the United States? That makes no business sense. Estimates are that US companies might buy about half of the oil, truck it to their refineries, and then resell the oil to other countries in the form of gasoline. Hence all the oil wouldn't necessarily go to Americans even if American-based companies bought it. See this: http://money.cnn.com/2013/09/16/news/economy/keystone-oil/
So that kills reason three right off the bat: the energy companies have no particular devotion to the United States. These companies are multinational. We shouldn't see prices come down much, if at all, because of increased supply caused by the XL Pipeline. Fact is, we already have excess supply and are are already shipping it to other countries in South America. (See article above.) I'd bet we'd continue to do so to keep demand here somewhat high.
Now, as you can see from the graphic, much of the pipeline already exists in the US. The logical thing to do is to investigate if the existing pipeline has caused any environmental damage, or what the likelihood of environmental damage might be. The environmental impact study requested by President Obama doesn't appear to have addressed that. It appears to have addressed how the pipeline might impact climate change in Canada. Conclusion? Probably not a lot. You can read a summary of the findings here, but it's also available online if you search for it. http://www.washingtonpost.com/business/economy/state-to-release-keystones-final-environmental-impact-statement-friday/2014/01/31/3a9bb25c-8a83-11e3-a5bd-844629433ba3_story.html
That's nice to know, but what Americans are concerned about is our land, our countryside, our rivers, our crops, our backyards, the Gulf. Seriously, I can't find much of anything but speculation. Those who support the pipeline say the risks are minimal. Those who don't say the risks are underestimated. But, I'm inclined to think other TransCanada pipelines are a decent indication of how this pipeline will behave, and voila! Twelve oil spills in the first year of operation here. Another similar company's tar sands pipeline spilled a million gallons of oil into the Kalamazoo River in Michigan in 2010, and despite clean up efforts there, about forty miles of that river are reported to still be contaminated. Why would the Keystone XL Pipeline be especially benign over any other? You decide: http://www.foe.org/projects/climate-and-energy/tar-sands/keystone-xl-pipeline
Finally, here is another summary of the supposed benefits of the pipeline with additional reasons those benefits are either outright falsehoods or grossly misstated: http://tarsandsaction.org/spread-the-word/key-facts-keystone-xl/
So... will our Congress and Senate continue pandering to Big Oil, or will our senators and representatives take care of Americans and this land we inhabit? I'm skeptical. Lately they just do what the money tells them to do.